1. Field of the Invention
The present invention relates to a chemical amplification resist composition suitably usable in the ultramicrolithography process such as production of VLSI or high-capacity microchip as well as in other photofabrication processes and capable of forming a highly defined pattern by using an electron beam or an extreme-ultraviolet ray, and a pattern forming method using the composition. More specifically, the present invention relates to a chemical amplification resist composition for use particularly in the process using a substrate having a specific underlying film, and a resist film, a resist-coated mask blank, a resist pattern forming method and a photomask each using the composition.
2. Description of the Related Art
In the microfabrication using a resist composition, with an increase in the integration degree of an integrated circuit, formation of an ultrafine pattern is required. To meet this requirement, the exposure wavelength tends to become shorter, such as from g-line to i-line or further to excimer laser light, and, for example, development of a lithography technique using an electron beam is proceeding at present.
As to the polymer compound or low molecular compound used for exposure to excimer laser light or electron beam, there are known various polymer compounds or low molecular compounds such as a narrow dispersive hydroxystyrene-based polymer (see, Japanese Patent No. 2,962,145), a hydroxystyrene-based polymer having a repeating unit corresponding to indene (see, JP-A-2006-201532 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)), a low molecular compound having two or more phenolic hydroxyl groups per molecule (see, JP-A-2010-107963), and a (meth)acrylic polymer having a glass transition temperature of 120 to 170° C. (see, JP-A-2005-31233).
In order to form an ultrafine pattern, thin film formation of the resist is necessary, but thinning of the resist film incurs deterioration of the dry etching resistance. Also, in electron beam lithography, the effect of electron scattering (forward scattering) in the resist film is recently reduced by increasing the accelerating voltage of the electron beam (EB). However, in this case, the electron energy trapping ratio of the resist film decreases, giving rise to reduction in the sensitivity, and the effect of scattering (back scattering) of electrons reflected on the resist substrate increases.
Particularly, in the case of patterning on a photomask blank used for semiconductor exposure, a light-shielding film containing a heavy atom is present below the resist, and the effect of back scattering attributable to the heavy atom is more prominent.
As one of the methods to solve these problems, use of a polymer compound having a polycyclic aromatic structure such as naphthalene is being studied (see, for example, JP-A-2008-95009 and JP-A-2009-86354).
However, with respect to the performance such as sensitivity and resolution, more improvements are demanded. The microfabrication using a resist composition is not only used directly to produce an integrated circuit but also applied, in recent year, to the fabrication or the like of a so-called imprint mold structure (see, for example, JP-A-2008-162101 and Nanoimprint no Kiso to Gijutsu Kaihatsu•Oyo Tenkai—Nanoimprint no Kiban Gijutsu to Saishin no Gijutsu Tenkai (Basics and Developments of Technology and Application of Nanoimprint—Fundamental Technology of Nanoimprint and Deployment of Leading-Edge Technology), Yoshihiko Hirai (compiler), Frontier Shuppan (issued June, 2006)). Therefore, it becomes an important task to satisfy high sensitivity, high resolution property (for example, high resolution, excellent pattern profile and small line edge roughness (LER)) and good dry etching resistance all at the same time, and this needs to be solved.